diag: Add support remote devices when running diag over sockets

Currently, SOCKET_MODE does not support targets with remote
devices. Modify code to appropriately identify and process
data from remote devices when running in SOCKET_MODE.

Additionally, the usb is being read unnecessarily from the HSIC
code when running in SOCKET_MODE. Make modifications to the
HSIC code to only read from the USB when running in USB_MODE.

Change-Id: I72f4428006e694091f2e4e86a7f699618bda3f95
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>